Examples of evolution of microstructure in ceramics and composites.

In this article we describe a number of studies involving the direct observation of microstructural evolution. In general these investigations were carried out to establish the mechanistic paths involved. The materials studied range from fibers being evaluated for use in high-temperature ceramic composites to energetic materials used as propellants. In particular we discuss the room temperature imaging of materials difficult to image by conventional means and the use of the chamber atmosphere to influence microstructural evolution. Imaging of hydroxyapatite formed by chemical means is briefly described as an example of a difficult microstructure. Microstructural evolution during calcium aluminate cement hydration relies on the chamber atmosphere to control moisture loss from the hydrating specimens. In some instances microstructural evolution with heating occurred independently of the chamber atmosphere. Grain growth in PZT films formed by sol-gel processes depends strongly on temperature but does not appear to depend on the chamber atmosphere. This is also the case for the combustion of nitroamine propellants in that their combustion does not depend on access to an external source of oxygen. In other studies, the chamber atmosphere played an indirect role in determining microstructure. However, the mechanistic path driving microstructural evolution in copper-based inks used as conductive paths on electronic substrates is atmosphere dependent. These inks are formulated from copper powder, glass, and an organic binder, and the interaction of the binder with an oxidizing atmosphere allows it to be burned out before significant interaction occurs between the copper powder and the glass. Finally, the microstructural variations during the oxidation of structural composites at high temperature were used to allow assessments of their likely failure mechanisms.

Impalement injuries of the palate in children: review of 131 cases.

Impalement injuries of the soft palate and oropharynx are common injuries especially in children. Devastating neurologic sequelae secondary to thrombus propagation in the internal carotid artery are rare but well-documented complications of these innocuous appearing injuries. Neurologic sequelae have been reported anywhere from 3 to 60 hours after the injury. Protocols that include hospitalization up to 72 hours have been advocated. In order to evaluate the effectiveness and practicality of such protocols, all hospital admissions for palate injuries in the past 17 years were reviewed. Of the 131 cases reviewed, no complications were discovered during hospitalization, nor were there any complications in these patients seen in follow up. Based on this review, the majority of soft plate and oropharyngeal impalement injuries can be managed on an outpatient basis. Parental counseling, similar to instructions given in instances of mild head trauma, as well as close follow up in the office are felt to be a more reasonable and as well as a safe treatment plan. A suggested instruction form is presented.